In interventional X-ray imaging, the detection of the instant when contrast agent arrives in the field of view is used for different applications. For example, in digital subtraction angiography (DSA), mask images may be selected prior to contrast injection. The detection of the instant when injection of contrast agent takes place has been shown to optimize the masking process. For example, EP 2 662 830 A1 relates to DSA and describes an evaluation step of calculating evaluation values indicating the states of the injection of the radiopaque dye for each of the frames constituting the DSA images. US 2012/0128226 A1 relates to automatic detection of contrast injection and describes the measure of image intensity to be determined for each of the subtracted images. In WO 2010/044001 A2, for visualizing an object of interest together with a device, a combined device and anatomy boosting is described. Since the device is already visible in X-ray imaging, the instant when contrast agent reaches the device, the contrast agent is used to visualize the anatomy. The arrival of the contrast agent is monitored in the vicinity of the device. WO 2008/104909 relates to recording a vascular structure during an intervention. An injection of a contrast agent provided to the vicinity of a device landmark is detected and the vicinity of the device landmark is monitored. Time contrast curves based on the monitored vicinity of the device landmark are generated and analyzed to determine a best instant as a visibility optimum based on the time contrast curves. The arrival of the contrast agent is looked for and analyzed in an area besides the device landmark.
However, it has been shown that this is not always easily possible and may also imply some delays, for example the first injected frames might only be weakly injected and hence the contrast arrival may be detected with a delay. It has been shown further that in certain interventions, real time minimally delayed injection detection is required.